The present invention relates to compounds able to inhibit calcium receptor activity and the use of such compounds. Preferably, the compounds described herein are administered to patients to achieve a therapeutic effect.
Certain cells in the body respond not only to chemical signals, but also to ions such as extracellular calcium ions (Ca2+). Extracellular Ca2+ is under tight homeostatic control and regulates various processes such as blood clotting, nerve and muscle excitability, and proper bone formation.
Calcium receptor proteins enable certain specialized cells to respond to changes in extracellular Ca2+ concentration. For example, extracellular Ca2+ inhibits the secretion of parathyroid hormone (PTH) from parathyroid cells, inhibits bone resorption by osteoclasts, and stimulates secretion of calcitonin from C-cells.
PTH is the principal endocrine factor regulating Ca2+ homeostasis in the blood and extracellular fluids. PTH, by acting on bone and kidney cells, increases the level of Ca2+ in the blood. This increase in extracellular Ca2+ then acts as a negative feedback signal, depressing PTH secretion. The reciprocal relationship between extracellular Ca2+ and PTH secretion forms an important mechanism maintaining bodily Ca2+ homeostasis.
Extracellular Ca2+ acts directly on parathyroid cells to regulate PTH secretion. The existence of a parathyroid cell surface protein which detects changes in extracellular Ca2+ has been confirmed. (Brown et al., Nature 366:574, 1993.) In parathyroid cells, this protein, the calcium receptor, acts as a receptor for extracellular Ca2+, detects changes in the ion concentration of extracellular Ca2+, and initiates a functional cellular response, PTH secretion.
Extracellular Ca2+ can exert effects on different cell functions, reviewed in Nemeth et al., Cell Calcium 11:319, 1990. The role of extracellular Ca2+ in parafollicular (C-cells) and parathyroid cells is discussed in Nemeth, Cell Calcium 11:323, 1990. These cells were shown to express similar calcium receptors. (See, Brown et al., Nature 366:574, 1993; Mithal et al., J. Bone Miner. Res. 9, Suppl. 1, s282, 1994; Rogers et al., J. Bone Miner. Res. 9, Suppl, 1, s409, 1994; Garrett et al., Endocrinology 136:5202-5211, 1995.) The role of extracellular Ca2+ on bone osteoclasts is discussed by Zaidi, Bioscience Reports 10:493, 1990.
The ability of various molecules to mimic extracellular Ca2+ in vitro is discussed in references such as Nemeth et al., in xe2x80x9cCalcium-Binding Proteins in Health and Disease,xe2x80x9d 1987, Academic Press, Inc., pp. 33-35; Brown et al., Endocrinology 128:3047, 1991; Chen et al., J. Bone Miner. Res. 5:581, 1990; and Zaidi et al., Biochem. Biophys. Res. Commun. 167:807, 1990.
Nemeth et al., PCT/US92/07175, International Publication Number WO 93/04373, Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959, and Nemeth et al., PCT/US94/12117, International Publication Number WO 95/11211, feature calcium receptor-active molecules and refer to calcilytics as compounds able to inhibit calcium receptor activity. For example, WO 94/18959 on page 8, lines 2-13 asserts:
Applicant is also the first to describe methods by which molecules active at these Ca2+ receptors can be identified and used as lead molecules in the discovery, development, design, modification and/or construction of useful calcimimetics or calcilytics which are active at Ca2+ receptors. Such calcimimetics or calcilytics are useful in the treatment of various disease states characterized by abnormal levels of one or more components, e.g., polypeptides such as hormones, enzymes or growth factors, the expresssion and/or secretion of which is regulated or affected by activity at one or more Ca2+ receptors.
The references provided in the background are not admitted to be prior art to the pending claims.
The present invention features calcilytic compounds. xe2x80x9cCalcilytic compoundsxe2x80x9d refer to compounds able to inhibit calcium receptor activity. The ability of a compound to xe2x80x9cinhibit calcium receptor activityxe2x80x9d means that the compound causes a decrease in one or more calcium receptor activities evoked by extracellular Ca2+.
The use of calcilytic compounds to inhibit calcium receptor activity and/or achieve a beneficial effect in a patient are described below. Also described below are techniques which can be used to obtain additional calcilytic compounds.
An example of featured calcilytic compounds are Structure I xcex1,xcex1-disubstituted arylalkylamine derivatives having the chemical formula: 
where
R1 is selected from the group consisting of: aryl, longer-length alk, and cycloalk;
R2 is selected from the group consisting of: lower alk, cycloalk, alkoxy, H, OH, xe2x95x90O, C(O)OH, C(O)O-lower alk, C(O)NH-lower alk, C(O)N(lower alk)2, SH, S-lower alk, NH2, NH-lower alk, and N(lower alk)2;
R3 and R4 is each independently lower alk or together cyclopropyl;
R5 is aryl;
R6 if present is either hydrogen, lower alkyl or lower alkenyl, wherein R6 is not present if R2 is xe2x95x90O;
Y1 is either covalent bond, alkylene, or alkenylene;
Y2 is alkylene;
Y3 is alkylene; and
Z is selected from the group consisting of: covalent bond, O, S, NH, N-lower alk, alkylene, alkenylene, and alkynylene, provided that if Z is either O, S, NH, or N-lower alk, then Y1 is not a covalent bond, further provided that Y1 and Z may together be a covalent bond;
and pharmaceutically acceptable salts and complexes thereof.
The terms aryl, longer-length alk, lower alk, cycloalk, alkoxy, alkylene, alkenylene, and alkynylene, along with possible substituents are defined in Section II, infra. Section II, infra, also provides definitions for other chemical groups described in the present application.
Preferred calcilytic compounds have an IC50xe2x89xa650 xcexcM, more preferably an IC50 less than 10 xcexcM, and even more preferably an IC50 less than 1 xcexcM, as measured using the xe2x80x9cCalcium Receptor Inhibitor Assayxe2x80x9d described in Example 1, infra.
Thus, a first aspect of the present invention features a method of treating a patient by administering to the patient a therapeutically effective amount of a Structure I xcex1,xcex1-disubstituted arylalkylamine derivative. Treatment can be carried out, for example, to retard the disease in a patient having a disease or to prophylactically retard or prevent the onset of a disease.
A therapeutically effective amount is the amount of compound which achieves a therapeutic effect by retarding a disease in a patient having a disease or prophylactically retarding or preventing the onset of a disease. Preferably, it is an amount which relieves to some extent one or more symptoms of a disease or disorder in a patient; returns to normal either partially or completely one or more physiological or biochemical parameters associated with or causative of the disease or disorder; and/or reduces the likelihood of the onset of the disease of disorder.
A xe2x80x9cpatientxe2x80x9d refers to a mammal in which compounds characterized by their ability to inhibit calcium receptor activity, in vivo or in vitro, will have a beneficial effect. Preferably, the patient is a human being.
Patients benefiting from the administration of a therapeutic amount of a calcilytic compound can be identified using standard techniques known to those in the medical profession. Diseases or disorders which can be treated by inhibiting one or more calcium receptor activities include one or more of the following types: (1) those characterized by an abnormal bone and mineral homeostasis; (2) those characterized by an abnormal amount of an extracellular or intracellular messenger whose production can be affected by one or more calcium receptor activities; (3) those characterized by an abnormal effect (e.g., a different effect in kind or magnitude) of an intracellular or extracellular messenger which can itself be ameliorated by one or more calcium receptor activities; and (4) other diseases or disorders where inhibition of one or more calcium receptor activities exerts a beneficial effect, for example, in diseases or disorders where the production of an intracellular or extracellular messenger stimulated by receptor activity compensates for an abnormal amount of a different messenger. Examples of extracellular messengers whose secretion and/or effect can be affected by inhibiting calcium receptor activity are believed to include inorganic ions, hormones, neurotransmitters, growth factors, and chemokines. Examples of intracellular messengers include cAMP, cGMP, IP3, calcium, magnesium, and diacylglycerol.
Preferably, a patient is a human having a disease or disorder characterized by one or more of the following: (1) an abnormal bone or mineral homeostasis; (2) an abnormal amount of an extracellular or intracellular messenger which is ameliorated by a compound able to effect one or more calcium receptor activities; and (3) an abnormal effect of an intracellular or extracellular messenger which is ameliorated by a compound able to effect one or more calcium receptor activities.
Preferably, the disease or disorder is characterized by an abnormal bone and mineral homeostasis, more preferably calcium homeostasis. Abnormal calcium homeostasis is characterized by one or more of the following activities: (1) an abnormal increase or decrease in serum calcium; (2) an abnormal increase or decrease in urinary excretion of calcium; (3) an abnormal increase or decrease in bone calcium levels, for example, as assessed by bone mineral density measurements; (4) an abnormal absorption of dietary calcium; (5) an abnormal increase or decrease in the production and/or release of messengers which affect serum calcium levels such as PTH and calcitonin; and (6) an abnormal change in the response elicited by messengers which affect serum calcium levels. The abnormal increase or decrease in these different aspects of calcium homeostasis is relative to that occurring in the general population and is generally associated with a disease or disorder.
Preferably, the calcilytic compounds are used to treat diseases or disorders selected from the group consisting of: hypoparathyroidism, osteosarcoma, periodontal disease, fracture healing, osteoarthritis, rheumatoid arthritis, Paget""s disease, humoral hypercalcemia malignancy, and osteoporosis.
Another aspect of the present invention describes a method of treating a patient comprising the step of administering to the patient an amount of a calcilytic compound sufficient to increase serum PTH level. Preferably, the method is carried out by administering an amount of the compound effective to cause an increase in duration and/or quantity of serum PTH level sufficient to have a therapeutic effect.
Increasing serum PTH may be used to achieve a therapeutic effect by retarding a disease in a patient having the disease or prophylactically retarding or preventing the onset of a disease. Prophylactic treatment can be performed, for example, on a person with an abnormally low serum PTH; or on a person without a low serum PTH, but where increasing PTH has a beneficial effect. An abnormally low serum PTH is a serum PTH level lower than that occurring in the general population, and is preferably an amount associated with a disease or the onset of a disease.
Increasing serum PTH levels can be used to treat different types of diseases including bone and mineral related diseases.
In different embodiments, the compound administered to a patient causes an increase in serum PTH having a duration up to one hour, about one to about twenty-four hours, about one to about twelve hours, about one to about six hours, about one to about five hours, about one to about four hours, about two to about five hours, about two to about four hours, or about three to about six hours.
In additional different embodiments, the compound administered to a patient causes an increase in serum PTH up to 0.5 fold, 0.5 to 5 fold, 5 fold to 10 ten fold, and at least 10 fold, greater than peak serum PTH in the patient. The peak serum level is measured with respect to the patient not undergoing treatment.
Another aspect of the present invention features Structure I calcilytic compounds.
Another aspect of the present invention features a pharmaceutical composition comprising a pharmaceutically acceptable carrier and a calcilytic compound decscribed herein. The pharmaceutical composition contains the calcilytic compouind in a form suitable for administration into a mammal, preferably, a human being. Preferably, the pharmaceutical comosition contains an amount of a calcilytic compound in a proper pharmaceutical dosage form sufficient to exert a therapeutic effect on a human being. However, multiple doses of pharmaceutical compositions may be used to treat a patient.
Considerations and factors concerning dosage forms suitable for administration are known in the art and include potential toxic effects, solubility, route of administration, and maintaining activity. For example, pharmaceutical compositions injected into the bloodstream should be soluble.
Another aspect of the present invention features a method of screening for Structure I xcex1,xcex1-disubstituted arylalkylamine derivatives able to inhibit calcium receptor activity. The method involves the steps of contacting a cell having a calcium receptor with a Structure I xcex1,xcex1-disubstituted arylalkylamine arylalkylamine derivative and measuring the ability of the compound to inhibit calcium receptor activity.
The screening method can be carried out in vivo or in vitro and is particularly useful to identify those Structure I xcex1,xcex1-disubstituted arylalkylamine derivatives most able to act as calcilytic compounds. In vivo assays include measuring a physiological parameter related to calcium receptor activity, such as serum hormone levels or serum calcium ion concentration. In vitro assays include measuring the ability of the calcilytic compound to affect intracellular calcium concentration, or cellular hormone secretion. Examples of hormones levels which can be affected by calcilytic compounds include PTH and calcitonin.
The calcilytic compounds described herein can be used as part of in vivo or in vitro methods. Preferably, the compounds are used in vivo to achieve a beneficial effect in a patient. Examples of in vitro uses, and other in vivo uses, include use in a method to identify other calcilytic compounds and use as a tool to investigate calcium receptor activity or the physiological effects of inhibiting calcium receptor activity in different organisms.